FR2783917A1 - TEMPERATURE SENSOR - Google Patents

Abstract

The present invention provides a temperature sensor comprising a thermistor-like element received in a metal housing and a mineral-insulated cable for acquiring signals from said thermistor element in which the mineral-insulated cable employs a ventilation structure which provides characteristics. stable resistance to the thermistor type element. The thermistor-like element (1) comprises a thermistor section (la), made of an oxide-type semiconductor, and electrode wires (1b) extending from the thermistor section (la). ) for acquisition of thermistor signals and is arranged on the end of a mineral insulated cable (2) and received in a metal cover (3). The mineral insulated cable (2) employs a structure in which electrically conductive wires (2b) connected to the electrode wires (1b) are insulated and held in a metal outer cylinder (2a) by insulating powder (2c) poured out in the outer cylinder (2a). A ventilation amount of at least 5 x 10-4 ml / MPa. dryness is ensured inside the outer cylinder (2a) at normal temperature.

Description

TEMPERATURE SENSOR

  The present invention relates to a time sensor.

  temperature incorporating a thermistor type element which is used to detect the temperature and, more precisely, to a temperature sensor having a resistance to heat up to a temperature of approximately 1000 C which

  is suitable for use in, for example, a cap-

  an exhaust gas temperature sensor which is installed on a catalytic converter and so on of an automobile exhaust system and detects abnormal temperatures or deterioration of the catalyst and so on. This type of temperature sensor typically includes a thermistor type element having a certain temperature / resistance characteristic at the end of a wiring element for the acquisition of signals from the thermistor. This section

  end is covered with a metal cylinder cover

  drique closed at the level of the lower part leading

  to a structure in which the thermis- type element

  tance is housed in the space formed by the metal cover-

  lique and the end section of the wiring element.

  Normally, by pouring an insulating powder into a space between an external metallic cylinder and conductive wires, the structure of the wiring element is such that the conductive wires are insulated and held

  in the outer cylinder, and these lead wires are con-

  connected to the wires of the electrodes arranged on the element of

thermistor type.

  Since a material of the component thermistor type

  the thermistor type element consists of a semi

  oxide type conductor, ohmic characteristics (temperature / resistance characteristics) of the section

  thermistor fluctuates in accordance with the pressure

  amount of oxygen from the ambient atmosphere of the element of

thermistor type.

  In this type of temperature sensor, since the thermistor type element is housed in the metal cover, the oxidation of a heat resistant metal occurs at high temperatures (for example 700 C and above) and the partial pressure of oxygen from

  the internal atmosphere decreases. In an atmosphere of reduction-

  severe tion, a phenomenon occurs in which oxygen is temporarily withdrawn from the oxide semiconductor of the thermistor section, resulting in a disturbance of the above resistance characteristics to

high temperatures.

  It is therefore necessary to provide that the thermistor type element is housed in a metal cover with appropriate ventilation to stabilize the characteristics of the thermistor. Here in the case

  a temperature sensor employing a double structure

  pipes in which the periphery of the cable element

  moreover covered with a metal cylinder, etc.,

  (for example, that described in FIG. 8 of the Japanese patent

  nais n 2 621 488, a ventilation path can be formed using the distance between the wiring element and the

metal cylinder.

  The most recent sensors must however detect

  accurately tering temperatures over low ranges

  temperature variation and carry out a market command

  che / stop to estimate the deterioration of a cataly-

  sister and so on, asking for a pretty response

  fast. Consequently, it is necessary to make that the diameter-

  be external to the temperature sensitive section either

  smaller to increase the response speed of the cap-

  tor. The previously mentioned double pipe structure

  is structurally complex and inappropriate for these purposes.

  On the other hand, in the case of a single pipe structure in which the end section of an element of

  wiring with a thermistor type element is only-

  ment covered with a cylindrical metallic cover with closed bottom part, although it is advantageous to make the external diameter of the temperature-sensitive section smaller, the ventilation path for the thermistor type element must then be trained to

  inside the wiring element.

  However, as previously mentioned, since the wiring element employs a structure in which the conductor wires are insulated and held in an outer metallic cylinder by insulating powder poured into the outer cylinder, one cannot expect to have good ventilation. In addition, when the outer diameter of the temperature sensitive section is made smaller to increase the response speed, since this requires that the wiring member has a diameter

  smaller, it becomes difficult to provide ventilation.

  Consequently, there is a need to clarify the amount of ventilation required to stabilize the characteristics of

the thermistor.

  Therefore, taking into account the above points, the object of the present invention is to provide a sensor for

  temperature incorporating a thermistor type element lo-

  ge in a metal cover and a wiring element for acquisition of signals from said thermistor type element, in which the wiring element employs

  a ventilation structure which provides characteristics

  ques stable resistance of the element type thermis-

  and propose a manufacturing process for a cap-

  temperature sensor incorporating such a structure

wiring element.

  As a result of the most recent studies conducted

  by the inventors of the present invention and focusing on it

  reading on the amount of ventilation of the heating element

  blage, it has been determined by experience that, if said quanti-

  ventilation tee is equal to or greater than a prescribed amount, stable strength characteristics of the

  thermistor are obtained, thereby leading to the reaction

  of the present invention. -

  The present invention provides a temperature sensor.

  ture provided with a thermistor type element comprising a

  thermistor section made of thermistor material

  mistance, of a wiring element comprising electric wires

  triconductive conductors coupled to said elements of ther-

  mistor, to acquire thermistor signals from

  from the thermistor type element, isolated and maintained

  in an external metallic cylinder, and a metallic cover

  cylindrical shell which receives said element of the thermal type

  mister has an opening at one end and is closed at the other end and connected to said external cylinder at said opening; wherein said wiring member provides a quantity of ventilation in said external cylinder of at least 5 x 10-4 ml / (MPa.sec) at

normal temperature.

  As a result, an amount of outdoor air based on

  the amount of ventilation prescribed previously selected

  can be introduced through the interior of the wiring element into the space in which the wiring element

  thermistor type is housed, formed by the metal cover

  that and the wiring element, with the effect of preventing the formation of a severe reducing atmosphere around the thermistor type element. Thus, in accordance with the present invention, a ventilation structure can be realized which provides stable characteristics of

  resistance of the thermistor element.

  The thermistor type element is preferably made up of

  made of thermistor material and electrode wire

  extending from the thermistor section for ac-

  quisition of thermistor signals. In this case, the

  electrode wires are connected to the conductor wires.

  In accordance with the experimental studies conducted by the inventors of the present invention, the amount of

  the aforementioned prescribed ventilation is preferably

  rate fixed at 1 x 10-3 ml / (MPa.sec) at normal temperature

  but still preferably fixed at 5 x 10- 3 ml / (MPa.sec)

at normal temperature.

  The inventors of the present invention have confirmed that the object of the present invention can be achieved

  provided that the amount of ventilation mentioned above

  above is fixed even if the external diameter of the cylinder

  external, i.e. the external diameter of the cable element

  reduction, is reduced to 3 mm or less and that the diameter ex-

  dullness of the outer cylinder is reduced to 2.5 mm or less.

  As first means of specific wiring element

  to obtain the amount of ventilation prescribed previously

  mentioned, the lead wires of the wiring element

  can be isolated and held on the cylinder ex-

  dull by pouring insulating powder into the cylinder ex-

  dull between said external cylinder and the conducting wires,

  the external cylinder being able to have a coefficient

  thermal expansion cient of 3 x 10-6 (/ C) or more

  larger than that of insulating powder.

  As a result, at an elevated temperature facilitating the formation of a reducing atmosphere, the insulating powder poured into the outer cylinder shrinks relative to the outer cylinder, allowing the formation of a gap

  which allows the amount of ventilation prescribed previously

  ment mentioned to be fixed between the outer cylinder and

  insulating powder. More specifically, ma-

  gnesium can be used as an insulating powder.

  In a temperature sensor in which the previously mentioned external cylinder has a coefficient of thermal expansion which is at least 3 x 10-6 / (C) greater than that of the insulating powder, the inventors of the present invention have determined by experience that the amount of ventilation is increased by heat treatment

  of the wiring element. The amount of ventilation before

  mentioned may be increased to at least the previously mentioned value by heat treatment of

  the wiring element at a temperature of at least 900 C.

  In temperature sensors, the wiring element typically lacks flexibility for bending purposes and so on due to the presence of the

  metallic outer cylinder. As a result, the wiring in-

  the temperature sensor and the external circuits is normally connected to the external circuits using output cables in which the cables are passed

  through flexible hoses from the cabling element

  blage. At this time, the connection between the output cables and the wiring element is protected from the outside by a protective element in order to prevent the entry of humidity and dust and to provide protection against impact.

external and so on.

  Thus, the exchange of air between the section receiving the thermistor type element and the exterior is carried out through each of the interiors of the wiring element, from

  the protective element and the external pipe of the output cables

  tie. In this type of structure, it is preferred to ensure that the inside of the external pipe of the outlet cables is well ventilated.

  Consequently, in a structure using cables

  output cables previously mentioned, it is preferred to have the output cables, such as a plurality of electrically conductive wires, covered with pipes

flexible external.

  In the present invention, since the cables in the external pipes are composed of a plurality of wires

  for the output cables, gaps are formed in

  be corresponding wires and between the external pipes and the wires. The amount of ventilation inside

  outer pipes due to the presence of these spreaders

  can be made much larger than the amount

  required ventilation of the previous wiring element

  mentioned, thereby eliminating any ventilation problem.

tion.

  Fig. 1 is a partial cross-sectional view

  cut out showing a temperature sensor in accordance with a first embodiment of the present invention. Fig. 2 is a cross-sectional view along

  the radial direction of the mineral insulated cable from the cap-

  temperature sensor shown in fig. 1.

  Fig. 3 is a cross-sectional view along the radial direction of the sensor output cables.

  temperature shown in fig. 1.

  Fig. 4 is a graph showing the relationship between

  the duration of the oxidation treatment and the amount of ventilation

  lation in the mineral insulated cable.

  Fig. 5 is a graph illustrating the relationship between

  be the number of cooling and heating cycles and the rate of change of the resistance value of the thermistor type element in a temperature sensor when

  the duration of the oxidation treatment is changed in the

wheat with mineral insulation.

  The following provides an explanation of the present invention through its preferred embodiments with reference to the drawings. In the present embodiment, the temperature sensor of the present invention is explained as being applied to a temperature sensor.

  exhaust gas temperature installed on a device

  automobile exhaust gas purifier

  such as a catalytic converter which detects an abnormal temperature

  male or deterioration of a catalyst. Since this cap-

  temperature sensor is mainly installed in the exhaust gas path of an automobile, the section

  temperature detection must have a certain re-

  heat resistance, some impact resistance to

  high temperatures, some resistance to life

  brations and so on so as to withstand temperatures

  high erasures of the order of, for example, 1000 C.

  Thus, a heat resistant material which is able to withstand such temperatures is also used

  in the temperature detection section and a design

  solid structural tion is employed. More recently, more accurate exhaust temperature detection has been required by engine control systems and there is a need for temperature detection with improved response times. Fig. 1 is a partially cut cross-sectional view of a first embodiment

  realization of a temperature sensor of the present in-

  vention designed to take into account appropriately

  these new applications to systems.

  The temperature sensor 100 mainly consists of

  Lement of a thermistor type element 1, a mineral insulated cable (wiring element) 2 to acquire the

  signals from the thermistor, from a metal cover-

  lique 3 (metal housing) which receives the element of thermistor type 1 in such a way that it is not in direct contact with the exhaust gases, of output cables 4 to connect the cable with mineral insulation 2 to external circuits, a flange 5 for fixing the sensor to the wall of the pipe 21 of the exhaust gas path and

  a sleeve (protective element) 6 which protects the

  connection between the mineral insulated cable 2 and the cables

output 4.

  In Fig. 1, the interior of the exhaust gas path 20 through which the exhaust gases flow is placed below the wall of the pipe 21 and

  the temperature sensing section of the temperature sensor

  rature 100, which is composed of the thermis- type element

  tance 1 and the metal cover 3 which receives it, is in-

  serée and fixed in a hole 22 comprising a threaded hole for-

  mé in the wall of the pipe 21 so as to be exposed to

  inside the exhaust gas path 20.

  Here, a conical section 22a is formed in the surface

  internal face of the hole 22 closer to the path of the exhaust gases 20 than to the part of the threaded hole. The cap-

  temperature sensor 100 is thus fixed in position in pres-

  on the collar 5 with a screw 23.

  The flange 5 is made of a heat-resistant metal (for example, SUS304). It is connected to the outside of the mineral insulated cable 2 and has a conical shape corresponding to the conical section 22a of the hole 22. When the sensor is fixed to the wall of the pipe 21, in addition to the fact that the exhaust gases cannot escape from the exhaust gas path 20 as a result of the flange 5 fitting securely in the conical section 22a, the sensor is supported

  in the hole 22 of the wall of the pipe 21.

  Then, the thermistor type element has a

  thermistor section la, which is formed by frying

  floor, in a cylindrical shape, of a thermis material

  tance having excellent heat resistance consisting of an oxide type semiconductor such as Mn-Cr

  and a pair of electrode wires lb incorporated by adjuster

  tightened by withdrawal in the thermistor section la.

  The pair of the electrode wires 1b is intended to acquire an output (resistance corresponding to a temperature) in the form of thermistor signals originating from the thermistor section la and is made of a wire material such as a wire platinum with excellent heat resistance and excellent characteristics

Release.

  The pair of electrode wires 1b is incorporated roughly

  securely in parallel in the direction of the axis of the co-

  lonne from thermistor section la at a mu-

  constantly constant (between the electrodes), and an extremi-

  tee of each wire extends from the thermistor section la. The ends extending from the pair

  electrode wires 1b are each electrically connected

  laser welding resistance tees etc. at the levels of the sections Ml indicated with an "x" in FIG. 1 to a pair of conductive wires 2b of a mineral insulated cable (wiring element) 2 to acquire outside

thermistor signals.

  A cross-sectional view in the direction ra-

  dial of the mineral insulated cable 2 is shown in FIG. 2. The mineral insulated cable 2 insulates and maintains a pair of conductive wires 2b made of metal, such as stainless steel, (SUS310S as an example) inside a cylindrical external cylinder 2 made of a metal , such as stainless steel (SUS310S in the example). In the present embodiment, the conducting wires 2b are insulated and held in an external cylinder 2a by pouring insulating powder (protective element) 2C consisting of MgO, A1203 and so on between the external cylinder 2a and each conducting wire 2b to

  inside the outer cylinder 2a.

  Since this mineral insulated cable 2 is made by repeating the stretch and annealing it from a material

  of large diameter and is in the state of small diameter at the

  ment of the use, the insulating powder 2c is packed to a high density and the two conducting wires 2b are

  held firmly in place. The external diameter of the cylinder

  dre external 2 (external diameter of the cable with mineral insulation

  2) is 3 mm or less and, in the example, the diameter

  be external 2a is in the form of a cylinder having an external diameter of 2.3 mm, a wall thickness of

  0.3 mm and a length of 60 mm. In addition, each wire con-

  conductor 2b has an external diameter of, for example,

0.3 mm.

  In addition, the mineral insulated cable ensures

  amount of ventilation inside the cylinder ex-

  dull 2a of at least 5 x 10-4 mm / (MPa.sec) at a normal temperature 1i when air (for example, industrial air) flows from one end to the other end at a pressure of 5 atm. This prescribed amount of ventilation can be obtained by appropriately selecting the particle diameter of the insulating powder 2c (for example, a diameter

  average particulate meter: 100 µm, a distribution of

  particle size: 75 to 150 µm), pouring the insulating powder in such a way with appropriate spacings

  can be formed and no compaction of the iso-

  even denser than necessary even after

  stretching the mineral insulated cable.

  In addition, it is preferred that the outer cylinder 2a

  be composed in such a way that its coefficient of di-

  thermal latation is at least 3 x 10-6 (/ C) higher than that of the insulating powder 2c in order to obtain the

  amount of ventilation prescribed previously mentioned.

  In the example, SUS310S is used as the material of the cy-

  external liner 2a and MgO (magnesium oxide) is used

  as insulating powder 2c and their dilation coefficients-

  respective thermal tion are 16.4 x 10-6 / C, for SUS310S and 13 x 10-6 / C for MgO over the range from room temperature to 400 C and 19.5 x 10-6 / C for SUS310S and 15 x 10-6 / C for MgO on the range of

  temperatures ranging from 400 C to 1000 C.

  In addition, the metal cover (metal case) 3 which receives the thermistor type element 1 is under the

  shape of a closed bottom cylinder made of a metal

  heat resistant such as SUS310S, has an opening

  ture 3a at a first end and a closed section 3b at

  the other end and has an external diameter of 3 mm.

  Thus, the temperature detection section of the present embodiment also has a narrow external diameter of 3 mm. In the example, the metal cover has a thickness of 0.3 mm and an internal diameter of

2.4 mm.

  The opening 3 of the metal cover 3 covers the external cylinder 2a and both the metal cover 2a

  and the outer cylinder 2a are fixed to this section of re-

  covering by circumferential welding by, for example, laser welding of the internal surface of the metal cover 3 and of the external surface of the external cylinder 2a (section indicated by the reference number M2 in FIG. 1). The opening 3a of the metal cover 3 is blocked by the mineral insulated cable 2 and the type element

  thermistor 1 is housed in the space formed in the cover

metal key 3.

  Then, a pair of output cables 4 are respected.

  tively connected using a connection process

  such as fitting or welding a pair of con-

* ductors 2b at a site on the opposite side compared to

  wearing alongside o the element of thermistor type 1 and the

  electrode wires lb are connected in the insulated cable

  mineral 2 (section M3 in Fig. 1). A cross-sectional view in the radial direction of the output cable 4 is shown in FIG. 3. This output cable

  4 consists of a plurality of electrically connected wires

  ductors 4a covered with a flexible external pipe 4b.

  In this way, since the wires 4a inside the external pipe 4b consist of a plurality of wires (7 are shown in the example of fig. 3), a spacing is formed as shown in fig. 3 between each of the corresponding wires 4a and between the external pipe 4b and

wires 4a.

  Here, the gaps formed in the output cables

  4 are sufficiently larger than the amount of ventila-

  prescribed above mentioned inside the ca-

  mineral insulated wheat 2 properly filled

with insulating powder 2c.

  In addition, the wires 4a can be made, for example, of a metal, such as stainless steel while the external pipe 4b can be made of a material.

  flexible such as ethylene tetrafluoride plastic.

  In the example, by twisting 7 wires having a diameter

  0.12 mm at least, each wire does not become tangled

  which, in addition to ensuring an improvement in the formability, improves the resistance of the output cables 4

  with respect to the curvature stress.

  The connection with a mineral insulated cable 2 (conductive wires 2b) to a pair of output cables 4 is protected from the outside by a sleeve 6. The sleeve 6 is in the form of a cylinder made of metal such as

  SUS304 and is arranged from the outside of the output cables

  tie 4 to the outside of the outer cylinder 2a.

  The sleeve 6 is fixed around the outside of the cylinder.

  dre external 2a by welding and so on to the surface

  outer of the flange 5 and is fixed in a tight

  rée by means of a rubber sleeve 7 to prevent the entry of water, dust and so on (section M4 in fig. 1) while also maintaining the interior

  hermetic sleeve 6. In this embodiment

  tion, a protective element is constituted by the sleeve 6

and the rubber sleeve 7.

  In addition, a coupler 8 is provided on the oppo-

  connected to the mineral insulated cable 2 (conductor wires 2b) in a pair of output cables 4 (section of the output port of the output cables) for connection to external circuits (such as a control unit vehicle electronics) or cable

  extending from an external circuit and so on.

  In the temperature sensor 100 having this structure, the output of the thermistor type element 1 is acquired with a pair of electrode wires 2b and then transferred to the external circuits after having been acquired by a unit external to the sensor using cables from

  output 4 from the mineral insulated cable 2.

  In addition, in the temperature sensor 100, the air inside the metal cover 3, namely at

  the interior of the section receiving the element of the therm type

  mistance 1, expands or contracts due to fluctuations in the temperature of the exhaust gases during use. It follows that the indoor air flows at

  from the spacings of the connection section of the

  weep 8 in the coupler 8, while the outside air flows in the coupler 8 from the con-

  tact with the outside air in the external circuits.

  That is to say, as shown by the dashed arrows in fig. 1, at some point

  the outside air flows in the coupler 8, in the gaps

  the output cables 4, in the sleeve 6, in the section containing the insulating powder 2c and in the element

  thermistor type 1, after which it flows into the sec-

  tion containing the thermistor type element 1. In addition, at some other time, the air around the thermistor type element 1 flows outward along the path

  opposite to that described above.

  In this way, since the present embodiment

  tion takes the inside of the mineral insulated cable 2, which is the section for determining the speed of the air flow previously mentioned to be the amount of prescribed ventilation previously mentioned, the air is effectively exchanged in the section containing l thermistor element 1 (inside of the metal cover 3), thereby preventing the atmosphere around

  of thermistor type 1 element could become an

  excessively reducing mosphere and can provide

  stable resistance characteristics to the thermistor element. Then, the mineral insulated cable 2, which is the essential component of the present invention, is manufactured by repeating a stretching and annealing carried out so

  programmed as previously described. As previously mentioned

  As mentioned, the distribution of the particular dimensions

  rooms are adjusted appropriately in advance to obtain the prescribed amount of ventilation. The mineral insulated cable 2 is then connected to the thermistor type element by resistance welding or welding

  laser wires the electrode lb of the thermis- type element

  sintered tance 1 to the conducting wires 2b.

  In the present embodiment, however, the cable

  wheat with mineral insulation 2 whole is heat treated at a temperature of 900 C or more to obtain a level

  even higher amount of ventilation than before

  ment mentioned in the mineral insulated cable 2. The basis for this is described based on an example

  of examining the relationship between the amount of yen-

  covering in the mineral insulated cable 2 and the charac-

  resistance characteristics of the thermis- type element

  tance. The mineral insulated cable 2 used the structure described in the previous example (external diameter: 2.3 mm) and was heat treated (treated for oxidation) at a temperature of 900 C while being assembled with the type element. thermistor 1 and metal cover 3. The ventilation rate (ml / sec) when air (for example, industrial air) was allowed to flow at

  a pressure of 5 atmospheres from one side to the other side

  t at normal temperature (approximately 25 C) has been

  converted in quantity by 1 MPa (ml / (MPa.sec)).

  Fig. 4 shows a graph of the relationship between the

  duration of the oxidation treatment (hr) and the amount of yen-

  tilation (ml / MPa.sec)). The oxidation treatment was ef-

  performed for 0, 40 and 100 hours, and two measurements were taken at each point over time. Furthermore, FIG.

  4 also shows a comparative example in which the cost

  tee air inlet of a mineral insulated cable treated for oxidation at a temperature of 900 C for 100 hours a

  been closed with an airtight closure element for

  basically catch the air flow.

  As shown in fig. 4, as a result of having carried out the treatment for oxidation, the amount of ventilation previously mentioned has increased beyond 5 x 10-4 (ml / MPa.sec) (equivalent to the value of the trace less than 0 hr the duration of the oxidation treatment over

  fig. 4) at normal temperature and the amount of ven-

  tilation has increased with an increase in the duration of

oxidation treatment.

  The results of the study of the characteristics of re-

  resistance of the thermistor type element 1 for each temperature sensor 100 in which the mineral-insulated cable has been treated for oxidation for 0.40 or 100 hours as described above are shown in Fig. 5. The

  Fig. 5 is a graph showing the relationship between the name-

  number of cooling and heating cycles (horizontal axis

  zontal) and the rate of change of resistance (axis ver-

  tical: rate of change r, units:%) indicating the rate of change of the initial resistance in the element of

  thermistor type 1 while applying the return cycles

  cooling and heating from 25 C up to 900 C at each

than temperature sensor 100.

  In Fig. 5, the temperature sensor treated for oxidation for 0 hr is shown with squares

  white and black, the temperature sensor treated for oxy-

  donation for 40 hours with white and black triangles and the temperature sensor treated for oxidation for hours with white and black circles. In addition, -a

  temperature sensor using mineral insulated cable

  rale of the previously mentioned comparative example in which all air is difficult to allow to flow by closing one end of the mineral insulated cable 2

is represented with an "x".

  As shown in FIG. 4, a ventilation quantity of at least 1 x 10-3 (ml / MPa.sec) was obtained at normal temperature during an oxidation treatment of 40 hours and a ventilation quantity of at least 5 x - 3 (ml / MPa.sec) was obtained at normal temperature

  during a 100 hour oxidation treatment.

  As shown in FIG. 5, all sensors

  of the temperature of this embodiment were used

  read in practice (for example, rate of change in resistance within 5%). The rate of change of

  resistance was favorably inhibited associated with increased

  indication of the duration of the treatment for oxidation,

  see an increase in the amount of ventilation and

  it was especially difficult to make any changes-

  rate of change in resistance over time

  100 hour oxidation treatment.

  Thus, although stable resistance characteristics

  The thermistor type element is obtained even if the mineral insulated cable 2 is not treated for oxidation since the quantity of ventilation prescribed above mentioned is obtained, it is preferred to obtain a quantity of ventilation of 1 x 10-3 (ml / (MPa.sec)) at normal temperature by performing the oxidation treatment and again preferably to obtain a ventilation quantity of 5 x 10-3 (ml / (MPa.sec) ) at

normal temperature.

  In addition, although the mineral insulated cable 2 can be heat treated alone, it is preferred to heat treat the entire assembly by assembling the thermistor A and the metal cover 2 with the cable to

  mineral insulation 2. This is intended to prohibit the fo-r-

  mation of a reducing atmosphere which has an unfavorable effect

  ble on the resistance characteristics of the thermistor type element at high temperatures by forming a

  stable oxide film on the inner surface of the metal cover

metal 3.

  In this way, in accordance with this mode

  embodiment, a ventilation structure can be realized

  line which provides stable resistance characteristics of the thermistor type element by obtaining the amount of ventilation prescribed previously mentioned in the mineral insulated cable 2 having an external diameter of 3 mm or less. In particular, in the example examined represented in FIG. 5, the stable characteristics of

  resistance of the thermistor type element have been con-

  firmed be obtained to the extent that the amount of sales

  the aforementioned prescribed coverage is reached for a narrower mineral insulated cable 2 having

an external diameter of 2.3 mm.

  In addition, in accordance with this embodiment

  Since the amount of ventilation is increased by heat treatment of the mineral insulated cable 2, the amount of ventilation prescribed previously mentioned can be achieved at a higher level. In addition, the amount of ventilation inside the outlet cables 4 can be sufficiently obtained by using a structure

  with the previously mentioned spacings.

  However, recently, in order to prevent the atmosphere around the thermistor element from becoming an excessively reducing atmosphere, studies have been carried out in the field of hermetic sealing of the structure of the assembly by developing elements. Of type

  thermistor with stable characteristics during

  only closed with a heat-resistant metal pipe which is resistant to the effects of the ambient atmosphere or by forming a stable oxide coating on the internal surface

  or resistant to heat-resistant metal pipe

  Health the area around the thermistor with an inert substance and some of these products are used in practice. However, even when using the method described above, since the hermetically closed thermistors simply comprise a structure of raw materials balanced in terms of their characteristics, if there is a variation in the structure, the characteristics are,

  correspondingly, susceptible to fluctuations.

  In the present embodiment, a temperature sensor

  higher structure is achieved in that it is able to stabilize

  ser the resistance characteristics of the thermistor type element even with regard to a structure similar to

that described above.

  (Other embodiments) In addition, although the wiring member in the form of a mineral insulated cable 2 employed a structure

  in which the conducting wires 2b are insulated and main-

  held in the outer cylinder 2a by pouring inside the outer cylinder 2a of insulating powder 2c between said outer cylinder 2a and the conductive wires 2b, the wiring element is not limited to that having such a structure.

  If the wiring element satisfies the two points

  resistant to employing a structure in which the electrically conductive wires 2b connected to the wires

  1b of a thermistor type element are iso-

  strips and are maintained in a metal cylinder 2a and to be able to achieve the prescribed amount of ventilation previously mentioned, the other sections can be

  constituted in any desired manner. For example-

  ple, insulating fibers where a porous element can be

  used as a holding element which insulates and

holds the wires.

  In addition, although the thermistor element is

  in the form of a so-called thermistor

  diale in which a pair of electrode wires lb extend in the same direction from the thermistor section lb in the present embodiment, the

  pair of electrode wires can extend in di-

  mutually opposite sections, one electrode wire being connected to the wiring element and the other wire

  electrode connected to the metal cover, get

  thereby providing what is called a thermistor

  axial, and the present invention can also be applied

  quée to what is called an axial thermistor. In other words, the number of the electrode wires can be any desired number and the conductive wires of the wiring element correspond to the number of electrode wires. In addition, the present invention can also be

  used in applications other than a time sensor

  exhaust gas temperature. The present invention is

  particularly suitable for use in a cap-

  temperature sensor having an external diameter of the temperature detection section of at least 3 mm and characterized by a rapid response. In addition, it is also suitable for use in a temperature sensor used over a temperature range from

  up to around 1000 C, at which temperature one atmo-

  reducing sphere tends to form easily around

the thermistor type element.

  Since the essential component of the present invention

  tion is the ventilation structure of the heating element

  blage, the design of the other sections can be natural-

Modified as required.

  The present invention is not limited by the specific embodiments described which can undergo considerable variations without departing from the scope of the invention.

Claims (10)

  1. A temperature sensor comprising: a thermistor type element (1) having a thermistor section (la) made of a thermistor material;   a wiring element (2) comprising electric wires   only conductors (2b) coupled to said thermistor type element (1), for acquiring the thermistor signals from the thermistor type element (1), isolated and held in an external metallic cylinder (2a); and a cylindrical metal case (3) which receives said thermistor type element (1), has an opening   (3) at one end and is closed at the other end   mite (3b) and is connected to said external cylinder (2a) at the opening (3a); in which,   said wiring element (2) fixes a quantity of sales   at least x 10-4ml / (MPa.sec) in said external cylinder (2a) at a normal temperature. 2. Temperature sensor according to claim 1, wherein the thermistor type element (1) comprises a thermistor section (la) made of a material of   thermistor and electrode wires (lb) extending through it   shot of the thermistor section (la) for acquisition of the thermistor signals, which electrode wires (lb)   are connected to said conductive wires (2b).   3. The temperature sensor according to claim 1 or 2, wherein an amount of ventilation of at least 1 x -3 ml / (MPa.sec)) is fixed.   4. The temperature sensor according to claim 3, wherein an amount of ventilation of at least 5 x 10-3 ml / (MPa.sec) is fixed.   5. Temperature sensor according to any one of   claims 1 to 4, wherein the outer diameter of said   outer cylinder (2a) is 3mm or less.   6. The temperature sensor according to claim 5, wherein the outer diameter of said outer cylinder (2a) is 2.5mm or less.   7. Temperature sensor according to any one of   claims 1 to 6, wherein said conductive wires   (2b) are insulated and held in the outer cylinder (2a) by filling the wiring element (2b) with insulating powder (2c) between said outer cylinder (2a) and said conductor wires (2b) inside of said outer cylinder (2a) and said outer cylinder (2a) has a coefficient of thermal expansion of at least 3 x 10-6 (/ C) more   larger than that of said insulating powder (2c).   8. Temperature sensor according to claim 7,   wherein said insulating powder (2c) is made es-   substantially of magnesium oxide.   9. A temperature sensor according to claim 7 or 8, which comprises said wiring element (2) of a sensor   temperature treated by thermal oxidation at a temperature erasure of 900 C or more.   10. Temperature sensor according to any one of   Claims 1 to 9, in which output cables (4)   for connection to external circuits are connected to said conductor wires (2b) at a site on the opposite side from the side at which said thermistor type element is coupled to said wiring element (2); the connection between said output cables (4) and said conductor wires (2b) is protected from the outside by protective elements (6,7) arranged from the outside of said output cables (4) up to the exterior of said outer cylinder (2a); and, said output cables (4) are essentially   made up of a plurality of electrically conductive wires   teurs (4a) covered by flexible cover pipes (4b).